The human heart represents a major organ with respect to morbidity and mortality among the population. In spite of increased knowledge and treatment of cardiovascular disorders myocardial infarction and coronary artery disease still represent major causes of death. Acute myocardial infarction was the primary cause of 25,023 deaths during 1992 in Sweden.
Microdialysis is used to monitor the interstitial fluid in various body organs with respect to local metabolic changes. The technique is now also experimentally applied in humans for measurements in adipose tissue (H. Rosdahl, U. Ungerstedt and J. Henriksson, "Microdialysis in human skeletal muscle and adipose tissue at low flow rates is possible if dextran-70 is added to prevent loss of perfusion fluid", Acta Physiol Scand, 1997, 159, pp 261-262), muscle (Rosdahl et al, as above, D. G. Maggs, W. P. Borg and R. S. Sherwin, "Microdialysis techniques in the study of brain and skeletal muscle", Diabetologia, 1997, 40: pp 75-82, Springer-Verlag and P. A. Jansson, J. Fowelin, U. Smith, and P. Lonnroth, 1988, "Characterization by microdialysis of intercellular glucose levels in subcutaneous tissue in humans", Am J Physiol 255, E218-E220.) and brain (Maggs el al, as above and R. Kanthan, A. Shuaib, G. Goplen and H. Miyashita, "A new method of in-vivo microdialysis of the human brain", Journal of Neuroscience Methods 60 (1995) 151-155). Routine use of microdialysis in clinical settings is, however, not yet established. Traditionally microdialysis catheters are inserted into the tissue and after an equilibration period, measurements of metabolic changes within the local tissue area can be made.
In U.S. Pat. No. 4,694,832, a dialysis probe is disclosed, which is primarily used for insertion into biological tissues, for example brain tissue. In such applications, the probe is located in the tissue through operation. It can also be inserted into a blood vessel or into tissue in the same manner as a canula and is then provided with a pointed, cutting edge. Consequently it is not suitable to be inserted into and guided by a blood vessel. Also the design of the dialysis chamber makes it unsuitable for insertion into and guidance by a blood vessel, since it is too fragile.
When admitted to a cardiac intensive care unit, patients with chest pain are routinely monitored by ECG and intermittent peripheral venous plasma markers (ASAT, ALAT, CK/CK-B, troponin-T and troponin-I ) for detection of cardiac damage. Regretfully though, the observed metabolic changes are usually detected late in the onset of myocardial infarction and angina pectoris. These markers are monitored in peripheral venous plasma by repeated blood sampling, and the response time is usually several hours. This halters the active treatment and intervention of ongoing myocardial ischaemia. Furthermore, a number of patients subjected to coronary surgery with CABG (coronary artery bypass grafting) or valve replacement have cardiac failure or associated diseases which increase the risk of the operation. These patients are post-operatively hemodynamically monitored in the intensive care unit but appropriate means of rapidly detecting metabolic disturbances in the heart are still lacking.
A continuous, rapid and selective monitoring of metabolic disturbance of the heart during ischaemia without repeated blood sampling would greatly enhance the possibilities of active intervention to prevent the development of myocardial infarction with non-reversible damage of the heart in patients admitted to cardiac intensive care units as well as in patients undergoing cardiac surgery.